Method and apparatus for defrosting refrigerators

ABSTRACT

IN A TWO-TEMPERATURE REFRIGERATOR WHEREIN THE DEFROSTING OF THE COOLER EVAPORATOR IS EFFECTED BY NATURAL THAWING DURING THE PERIODIC INOPERATIVE PERIODS OF THE REFRIGERATING APPARATUS IN ORDER TO EXPEDITE SAID DEFROSTING, THE LIQUID REFRIGERANT PRESENT IN THE COOLER EVAPORATOR UPON STOPPAGE OF THE COMPRESSOR IS FORCED INTO THE FREEZER EVAPORATOR BY PNEUMATIC PRESSURE GENERATED BY THE EVAPORIZATION OF A SMALL QUANTITY OFF LIQUID REFRIGERANT INTRODUCED INTO THE COOLER EVAPORATOR THROUGH A CAPILLARY TUBE AT THE BEGINNING OF THE INOPERATIVE PERIOD.

Dec. 14, 1971 BAUKNECHT ETAL 3,626,701

METHOD OF AND APPARATUS FOR DEFROSTING REFRIGERATORS Filed April 23, 1970 2 Shoots-Shoat 1 FIG] Dec. 14, 1971 BAUKNECHT EIAL 3,626,707

METHOD OF AND APPARATUS FOR DEFROSTING mwurunmvrons Filed April 25, 1970 2 Shoots-Shoat 3 United States Patent O 3,626,707 METHOD AND APPARATUS FOR DEFROSTING REFRIGERATORS Gottlob Bauknecht, Stuttgart, and Karl Laszlo, Welzheim,

Germany, assignors to Gottlob Bauknecht Elektromotorenbau, Stuttgart, Germany Filed Apr. 23, 1970, Ser. No. 31,166 Claims priority, application Germany, Apr. 23, 1969,

P 19 20 513.1 Int. Cl. FZSd 21/00 US. Cl. 62-81 11 Claims ABSTRACT OF THE DISCLOSURE In a two-temperature refrigerator wherein the defrosting of the cooler evaporator is effected by natural thawing during the periodic inoperative periods of the refrigerating apparatus in order to expedite said defrosting, the liquid refrigerant present in the cooler evaporator upon stoppage of the compressor is forced into the freezer evaporator by pneumatic pressure generated by the evaporization of a small quantity of liquid refrigerant introduced into the cooler evaporator through a capillary tube at the beginning of the inoperative period.

BACKGROUND OF THE INVENTION AND DEFINITION OF TERMS This invention relates to a method of and an apparatus for defrosting an evaporator which is associated with the normal (refrigerating) compartment of a two-temperature refrigerator and which is part of the refrigerant circuit of a compressor-type refrigerating apparatus. The refrigerant circuit also includes, in series with the aforenoted evaporator, a further evaporator associated with the freezer compartment of the refrigerator.

Hereinafter, the regular refrigerating compartment of the refrigerator will be designated as cooler compartmen and the evaporator associated therewith, as cooler evaporator. Also, the evaporator associated with the freezer compartment of the refrigerator will be designated as freezer evaporator.

The cooler evaporator lowers the temperature of the cooler compartment to about 3-7 C. above the freezing point of water, whereas the freezer evaporator seeks to maintain the temperature of the freezer compartment at approximately 18 C. below the freezing point of water.

The refrigerating apparatus is thermostatically controlled and has, accordingly, alternating operative and inoperative periods.

During each inoperative period of the refrigerating apparatus, the cooler evaporator is defrosted at least substantially by natural heating (i.e. by the air surrounding the evaporator) and further, the refrigerant, during the operation of the compressor, is first passed through the cooler evaporator and subsequently through the freezer evaporator.

A defrosting process of the aforenoted type, wherein the cooler evaporator is not thawed by artificial heating means, has significant advantages as compared with defrosting processes using artificial heat. Thus, no electrical energy is used for the defrosting, whereby significant operational costs are saved and, further, the structure of the refrigerating apparatus is simpler.

It is, however, a difficulty of this so-called natural defrosting" process that the duration of the individual de- 3,626,707 Patented Dec. 14, 1971 OBJECT AND SUMMARY OF THE INVENTION It is a principal object of the invention to provide an improved method of an apparatus for defrosting a refrigerator wherein the natural defrosting of the cooler evaporator is expedited, the inoperative periods of the refrigerating apparatus necessary for the defrosting are shortened and the temperature conditions in the freezer and the cooler are improved in a simple and operationally safe manner.

Briefly stated, according to the invention, subsequent to the beginning of each inoperative period of the refrigerating apparatus, the liquid refrigerant present in the cooler evaporator is driven therefrom into the freezer evaporator by means of pneumatic pressure generated by a small amount of refrigerant which flows after the deenergization of the compressor (i.e. at the beginning of the inoperative period of the refrigerator apparatus) in a liquid state through a capillary tube into the cooler evaporator and is evaporated therein. The refrigerant is driven by said pressure over a peak constituting a barrier which prevents any backflow of the refrigerant.

For practicing the afore-outlined method, there is provided a two-temperature refrigerator including a cooler evaporator and a freezer evaporator connected to the same compressor; the conduit system of the cooler evaporator extends, from its inlet, with a height drop to a lowest location. According to the invention, there is provided a capillary tube which terminates at a high location of said conduit system and further, there is provided a coupling conduit which connects the cooler evaporator with the downstream arranged freezer evaporator in such a manner that it extends from the lowest location of the cooler conduit system first upwardly over a peak and therefrom to the inlet of the freezer evaporator. The diameter of the coupling conduit portion between said lowest location and said peak is so designed that the said pneumatic pressure may not escape through the liquid column which is to be driven thereby into the freezer evaporator upon the beginning of the inoperative period of the refrigerator apparatus.

The invention will be better understood, as well as further objects and advantages will become more ap parent, from the ensuing detailed description of the method and of a preferred, although exemplary embodiment of the invention taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of a refrigerating apparatus according to the preferred embodiment of the invention;

FIG. 2 is a front elevational view of a household refrigerator with the door removed, incorporating the preferred embodiment, and

FIG. 3 is a fragmentary front elevational View of an enlarged detail of the preferred embodiment.

CHARACTERISTICS AND ADVANTAGES OF THE METHOD ACCORDING TO THE INVENTION The liquid refrigerant present in the cooler evaporator at the beginning of each inoperative period of the refrigerating apparatus, is blown from the cooler evaporator into the downstream connected freezer evaporator by the pneumatic pressure generated by the evaporation of a small quantity of liquid refrigerant introduced into the inlet of the cooler evaporator through a capillary tube subsequent to the stoppage of the compressor. Thus, for a transfer of refrigerant from the cooler evaporator to the freezer evaporator, it is not necessary to vaporize and then recondense the liquid refrigerant.

Were such an exaporation of the liquid refrigerant in the cooler evaporator necessary, then the cooler evaporator would be submitted to a continued cooling effect during the inoperative period of the compressor until the entire liquid refrigerant is evaporated. This would usually last several minutes and only thereafter could a natural defrosting take effect.

By the afore-stated inventive method, however, the period necessary for the natural defrosting (i.e. without artificial heating) and thus the inoperative period of the compressor are significantly shortened. The temperature conditions in the freezer compartment and in the cooler compartment are also improved. Further, the evaporators, because of the shorter inoperative periods, may be of smaller dimensions than those used in known refrigerators wherein the cooler evaporator is defrosted by natural means. Further, the temperature constant of the freezer compartment is additionally improved by the fact that a recondensation of the refrigerant vapors in the freezer compartment during the inoperative period does not take place.

The quantity of the refrigerant to be introduced through a capillary tube into the cooler evaporator subsequent to the stoppage of the compressor for blowing out the liquid refrigerant should preferably be no more than what is necessary for generating, upon evaporation, a pneumatic pressure that is sufficient to force out the entire liquid refrigerant present in the cooler evaporator after the stoppage of the compressor. For the purpose it is expedient to provide a vertical arrangement of the drier usually connected downstream of the liquefier.

The capacity of the freezer evaporator for the liquid refrigerant is preferably designed in such a manner that it is capable of accommodating, in addition to the liquid refrigerant already contained therein, the entire quantity of the refrigerant displaced from the cooler evaporator subsequent to the beginning of the inoperative period of the compressor, without thereby causing an over-flow into the suction conduit. For this purpose, the conduit system of the freezer evaporator may be provided in a known manner with accumulating means.

DESCRIPTION OF THE PREFERRED EMBODIMENT The refrigerating apparatus depicted in FIG. 1 includes an electric circuit in which there is connected a compressor 11, and further includes a liquefier 12, a vertically disposed drier 13, downstream of which there begins a capillary tube 14. As best seen in FIG. 3, the capillary tube 14 is introduced at 15 into an upwardly closed inlet tube 16 of a plate-type cooler evaporator generally indicated at 18. The refrigerating apparatus further includes a U-type freezer evaporator 19, an accumulator 20 associated therewith and a suction conduit 21. The cooler evaporator 18 has a tube coil 17 extending with a continuous drop from the vertical inlet tube 16 to a lowest location 23 and a tube portion 24 extending upwardly from the lowest location 23. The upper terminus of the tube portion 24 constitutes the outlet 26 of the cooler evaporator 18 and is connected to an intermediate channel 25. The latter, in turn, is coupled with an upwardly extending leg of an inverted U-shaped conduit which serves as a peak gate or barrier 28. The other, downwardly extending leg of the U-shaped conduit is connected with the inlet of the freezer evaporator generally indicated at 19. As shown, the gate 28 is disposed higher than the accumulator 20 and also higher than the conduit system of the freezer evaporator 19 arranged between the accumulator 20 and the gate 28.

The vertically arranged cooler evaporator 18 has a relatively large surface and extends, as best seen in FIG. 2, substantially along the entire height and width of the rear wall of the cooler compartment 30 of a householdtype refrigerator generally indicated at 31. The latter also comprises a freezer compartment 32 disposed adjacent above the cooler compartment 30. The cooler evaporator 18 operates as a pre-evaporator, whereas the freezer evaporator 19 forms the complementary evaporator of the refrigerating apparatus. The two evaporators 18 and 19, are, as described above, interconnected by means of the intermediate channel 25 which has a small flow resistance.

The plate-type cooler evaporator 18 includes an evaporator plate 33 (FIG. 3) made, at least substantially, of a synthetic material in which the tube coil 17 and the tube portion 24 are embedded. The plastic evaporator plate 33 may be formed of two layers between which there are embedded thin aluminum strips 34 in a heat conducting contact with the tubes 17, 24 for the equalization of the temperature of the plate evaporator. As Sl'lOWIl, the capillary tube 14 is introduced into the evaporator 18 at the highest location thereof, so that the refrigerant flows downwardly in the tube coil 17. The illustrated design and arrangement of the cooler evaporator 18 and the introduction of the capillary tube 14 in an upper range thereof are particularly advantageous features for the pneumatic cleaning of the evaporator subsequent to the beginning of the inoperative period of the compressor 11.

The periodic energization and de-energization of the compressor 11 is effected by a thermostat generally indicated at 36, the temperature sensitive element 37 of which is arranged on the evaporator plate 33 of the cooler evaporator 18 as shown in FIG. 1. The temperature responsive element 37 is, similar to the other components of the thermostat, of known structure and cooperates with a setting member 39 which actuates a switch 40 for the opening and closing of the electric circuit 10 of the compressor 11 as a function of the temperature sensed by the temperature responsive element 37. The compressor 11 is energized if the element 37 senses a temperature above 0 C., for example, +5 and is deenergized if a predetermined lowest temperature, for example, 10 C. is sensed.

It is ensured that by the natural thawing effect of the temperatures (usually between +3 and +7 C.) of the cooler compartment 30, the cooler evaporator 18 is at least substantially defrosted during the inoperative period of the refrigerator prior to the successive energization of the compressor 11.

In the inlet range where the terminal portion of the capillary tube 14 is in heat exchange relationship with the cooler evaporator 18, the warm liquid refrigerant present in the capillary tube has a heating effect on the evaporator 18. However, such heating effect is restricted to said inlet range. On the other hand, in the outlet range of the cooler evaporator 18 temperatures are particularly low because of the pressure drop during the operation of the compressor 11. In order to avoid this disadvantage and to improve the defrosting effect of the outlet range of the evaporator 18 as well, in the cooler evaporator 18 shown in FIGS. 2 and 3, the two tube portions 45 and 46, which respectively form the inlet and the outlet of the evaporator 18, are disposed at a small distance from one another, so that the higher temperature generated by the warm refrigerant flowing through the capil lary tube 14 is transferred from the tube 45 to the outlet range 44 cooled by the channel 26. It is therefore advantageous to arrange the opening 42 of the capillary tube 4 as shown within the range of the evaporator plate 33 at a distance from the edge 47 thereof.

As seen in FIG. 2, the gate 28 is disposed above the upper face of the freezer evaporator 19.

OPERATION OF THE PREFERRED EMBODIMENT and warmed. The liquid, warm refrigerant then flows through the drier 13 and through the capillary tube 14 and enters the vertically arranged cooler evaporator 18 approximately at its highest location. The liquid refrigerant emerging from the outlet opening 42 of the capillary tube 14 begins to boil and partially evaporates in the tube coil 17 as well as in the tube portion 24. This evaporation process draws heat from the cooler compartment, whereby a cooling effect is generated. The liquid refrigerant leaving the evaporator 18 through the intermediate channel 25 is introduced into the freezer evaporator 19 and is evaporated in the latter for cooling the freezer compartment. The latter is cooled to a substantially lower temperature than the cooler compartment.

From the freezer evaporator 19 the refrigerant, which, as a rule, is completely evaporated, passes through the accumulator 20 and the suction conduit 21 and returns into the compressor 11. The cooler evaporator 18 gradually cools during the operative period of the compressor 11. The temperature responsive component 37, upon sensing a predetermined lowest evaporating temperaure, de-energizes the compressor 11, so that the forced oirculation of the refrigerant is interrupted. The liquid, warm refrigerant which is present in a very small quantity in the capillary tube 14 at the moment the compressor 11 is de-energized, is capable of flowing, at least partially, from the capillary tube 14 into the cooler evaporator 18 where it evaporates.

By virtue of this evaporation, a vapor pressure (pneumatic pressure) is built up in the tube coil 17. This pressure buildup is isolated from the freezer evaporator 19 by the liquid refrigerant accumulating in the lowest location 23 of the cooler evaporator 18. Said pressure forces the column of liquid refrigerant, stagnant since the de-energization of the compressor 11, from the cooler evaporator 18 through tube portion 24, intermediate conduit 25 and gate or barrier 28 into the freezer evaporator 19. Here the liquid refrigerant accumulates.

The diameter of the tube 24 and that of the intermediate channel 25 is so designed that the pneumatic excess pressure generated upstream of the liquid column may not escape through the liquid column, but pushes the latter in front of it through the gate 28 into the freezer evaporator 19 so that the cooler evaporator 18 is entirely emptied.

The accumulator 20 serves as a safety chamber, so that during the inoperative period of the compressor 11, no liquid refrigerant may be admitted into the suction conduit 21 where it would cause undesired formation of water condensates and would also cause an increase of the operational costs. Since already after a short time subsequent to the de-energization of the compressor 11, the cooler evaporator 18 is practically entirely free of liquid refrigerant, the cooling effect thereof is rapidly discontinued and thus the thawing effect of the temperatures of the cooler compartment begins without a long delay. Thus, the cooler evaporator is rapidly defrosted. Upon termination of the defrosting, which is sensed by the temperature responsive component 37, the compressor 11 is again energized, whereby the afore-described cycle is repeated.

In view of the fact that during each inoperative period of the refrigerating apparatus, the cooler evaporator is practically entirely evaporated, the layer of frost present at the beginning of each inoperative period is very thin and can thus be rapidly thawed.

In addition to effect a rapid defrosting of the cooler evaporator, the afore-described method and apparatus has a temperature stabilizing effect on the freezer evaporator, since the additional liquid refrigerant forced thereinto during the inoperative period of the refrigerating apparatus slowly evaporates and thus continuously generates cold therein.

What is claimed is:

1. In a method of defrosting the cooler evaporator of a refrigerating apparatus of the known type having a refrigerant circuit that includes in series a compressor having alternating operative and inoperative periods, a cooler evaporator defrosted by natural thawing during said inoperative periods ad a freezer evaporator, the improvement comprising the steps of (A) generating a pneumatic pressure in said cooler evaporator at the beginning of each said inoperative periods and (B) forcing the liquid refrigerant present in said cooler evaporator at the beginning of each said inoperative periods into said freezer evaporator by means of said pneumatic pressure.

f2. A method as defined in claim 1, including the steps 0 (A) introducing a small amount of liquid refrigerant into said cooler evaporator at the beginning of each said inoperative periods and (B) evaporating said small amount of liquid refrigerant in said cooler evaporator to generate said pneumatic pressure.

3. A method as defined in claim 1, wherein said step (B) includes driving said refrigerant through a peak barrier which prevents said refrigerant from flowing back into said cooler evaporator during said inoperative periods.

4. In a refrigerating apparatus of the known type that includes a refrigerant circuit in which there is connected in series a compressor, a cooler evaporator and a freezer evaporator, the improvement comprising,

(A) a first conduit means included in said circuit and forming part of said cooler evaporator, said first conduit means having (1) an inlet end portion, (2) a lowest location, and (3) an outlet end portion,

(B) a second conduit means forming part of said circuit and connected downstream of the outlet of said first conduit means and upstream of said freezer evaporator, said second conduit means constituting a peak barrier being at a location higher than said first conduit means, and

(C) a capillary tube disposed in said refrigerant circuit and extending into said inlet end portion of said first conduit means.

5. An improvement as defined in claim 4, wherein said second conduit means is of inverted U-shape.

6. An improvement as defined in claim 4, including a third conduit means forming part of said refrigerant circuit and connected upstream of said second conduit means and downstream of said outlet end portion of said first conduit means, the diameter of said third conduit means and of that portion of said first conduit means that extends from said lowest location to said third conduit means are so designed that the pneumatic pressure generated in sa d first conduit means by the evaporation of liquid refrlgerant introduced into said inlet end portion of said first conduit means through said capillary tube at the beginning of each said inoperative period is prevented from escaping through said third conduit means and said lastnamed portion of said first conduit means.

7. An improvement as defined in claim 4, wherein said second conduit means is disposed at a location higher than said freezer evaporator.

8. An improvement as defined in claim 4, wherein said cooler evaporator is constituted by a plate-type evaporator.

9. An improvement as defined in claim 4, wherein said inlet end portion and said outlet end portion of said first 7 8 conduit means are disposed in a heat exchange relation- References Cited ship with respect to one another. D UNITED STATES PATENTS 10. An improvement as defined in claim 9, wherein the end portion of said capillary tube is so disposed in said ilgbacker inlet end ort'on of said first conduit means as to warm r nomague p l 5 2,986,901 6/1961 Hubacker 6251] the latter for increasing the temperature in said outlet end portion of said first conduit means.

11. An improvement as defined in claim 8, wherein said WILLIAM Pumary Examiner capillary tube has an outlet terminus disposed within the US Cl X outline of an evaporator plate of said cooler evaporator 10 at a distance from the outer edges thereof. 62151 277, 511, 8O 

